Dual focus x-ray apparatus



Nov. 14, 1950 c.. M. sLAcK 2,530,182

DUAL FOCUS X-RAY APPARATUS Filed June l5, 1944 IPM-gg .6. VaLr/vaf-INVENTOR imi' c. M. s4/Qca.

BY www ATTORNEY Patented Nov. 14, 195() DUAL FOCUSX-RAY APPARATUSCharles M..Slack, Glen Ridge, N. J., Vassigner -to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of PennsylvaniaApplication June 15, 1944, Serial'No. 540,384

(Cl. Z50-98) 9 Claims.

VThe present invention relates to X-.ray apparatus .and moreparticularlyto such apparatus employing a double-focusX-ray tube.

It is .now quite customary in the art to utilize an X-ray tube providedwith two lamentary cathodes, one which produces a small focal spot bythe passage of a relatively low current therethrough, thus adapting thetube for long exposures for purposes of uoroscopy, and a second highercurrent lamentary cathode which produces a larger focal spot forradiographic purposes. X-ray tubes of this type have proved quitesatisfactory in saving the cost of an extra tube and wherein there is asucient interim between the two types of diagnostic examinations.

"There are many instances, however, where the roentgenologist observessome phenomenon during `the course of a luoroscopic examination andwishes to immediately make a permanent record thereof by the making of aradiographic exposure.` This necessitates switching from thelowemission-small-focal-spot cathode to the highcurrent-large-focal-spotcathode. The disadvantage heretofore existent in such apparatus residesin the fact that it takes approximately a Vsecond or so for thehigh-current-large-focalspot-cathode to reach an electron emittingtemperature before "the radiographic exposure can be made. Consequentlythis lapse of one second is a serious handicap in many instances becausethe particular organ previously observed during uoroscopy may change inposition, shape or conditi-on, in performing'its natural function, sothat a radiographtaken after the lapse of one second may not show thesame condition intended to be radiographed.

- It is accordingly an object of the present invention to provide anX-ray apparatus employing a double-focus X-ray tube wherein the changefrom one focal spot to the other for the making of a radiographicexposure is accomplished without substantially any loss of time.

Another object of the present invention is the provision of an X-rayapparatus employing a double-focus X-ray tube wherein the high-cur-.rent-large-iocal-spot cathode is heated substantially instantaneouslyto an electron emitting temperature.

Still further objects of the present invention will become obvious tothose skilled in the art by reference to the accompanying drawingwherein: .Y Figure 1 is a schematic diagram of an X-ray apparatusconstructed in accordance with the present invention, and Y Figure 2 isa schematic diagram of -a modication which `the X-ray apparatus `asshown in Fig. 1 may take.

Referring now -to the drawings in detail, an X-ray tube l5 is shownwhich is provided with an anode 6, a -low-current-small-focal-spotlamentary cathode l, and a high-current-large-focalspotlamentarycathcde- 8. The X-ray tube recei-ves electrical energy from ahigh potential transformer 9, having its primary winding IIl connectedtoa source of the Ycustomary 'commercial potential of `11B-23d voltsthrough a suitable control'arra-ngement as noted by the legend. Thesecondary winding AI'2`is connectedthrough avbridge-arrangement ofrectifying valve tubes I3 tothe anode 'E and a connection I l common tobcthrlamentary cathodes 'I and'S, inthe usual manner of full wave X-raytube energizing circuits. 7 Y' rFor the purpose of heating the smallvfocalspot iilamentary cathode I to an electron emitting temperature, itis connected to the ysecondary winding I5 of -a low tension 'heatingvtrainsformer I6, and in a similar manner the larger focal-spoti'llamentary cathode 8 is connected to the secondary winding YVI -ofanother low tension heating Ytransformer I8. As shown, one end of theprimary winding I9vof transformer I6 is connected to a conductor 2liextending through a switch 221to a suitable sou-roe of supply'designatedLI, L2, such as the same ccmmercialsource adjustable impedance such 'asa resistance '29 and conductor SII-to the conductor'24 constituting thelother side of the supply source LI. Accordingly,

uponY closure ofswitch 22 both the primary windings IS and 28 areenergized. However, the adjustable resistance '23 is so set that thesecondary winding l5V delivers sufiicient energy to the smallfocal-spot-cathode 'I to heat it to an electron emitting temperature,`while the adjustable resistance 2-9 is set so that the secondary winding-I'I delivers just suiiicient Senergy to the largeA focal-spotcathode 8as'to maintain it at a tem'- The 'remaining end of primary windperaturewhere no electron emission occurs. Under these conditions, the X-raytube is conditioned for fluoroscopy and the operator merely operates thecustomary controls which causes energization of the high voltagetransformer 9 as desired.

When a radiographic exposure is desired, the diagnostician de-energizesthe high voltage transformer 9 and moves a lm carrying cassette into theeld of X-radiations from the tube in place of the fluorescent screen orin supermDOSSd position with respect thereto. Movement of the cassetteinto a position for a radiographic eX- posure is normally utilized toclose the requisite switches to change the apparatus from iiuoroscopicsetting to a radiographic setting, or they may be manually operated, asdesired. However, for the sake oi simplicity such switches are shownschematically in the present drawings.

Assuming now it is desired to make a radiographic exposure with theapparatus of the present invention and a cassette is moved into thefield of radiations after de-energization of the X-ray tube. A switch 32is then closed which completes a circuit from the conductor 2l(constituting one side of the supply source Ll) through a conductor 33,now momentarily closed pushed button switch 32, a normally closed switch34 to the winding 35 of a relay 36, and thence to conductor 20(constituting the other side of the supply source L2). The relay 36 isthus energized and raises its armature.

Movement of the armature of relay 36 interrupts the circuit to theprimary winding i9 of low tension transformer i6 by opening its normallyclosed contact 26, thus de-energizing the small focal-spot cathode l. Asecond relay contact 3l closes which completes a self-holding circuit torelay winding 35 by short-circuiting the momentary contact button 32through a conductor 36, and at the same time short-circuits theadjustable resistance 29, by means of a conductor 39, since the lattertogether with the conductor 38 constitute in eect an extension of theconductor 33, upon closure of relay contact 31.

Short-circuiting of the adjustable resistance 29 thus applies full linevoltage to primary winding '28 of the low tension transformer i8 causingthe secondary winding Il to deliver suiicient energy to the largefocal-spot cathode to raise it to an electron emitting temperature. Theapparatus thus far described diers very little from the prior art sinceit is known that by preheating the large focal-spot cathode to atemperature just below electron emission shortens the time required toraise it to an electron emitting temperature upon the furtherapplication of suilicient electrical energy thereto. Despite suchpreheating, however, a lapse of approximately one second occurs beforethe large focal spot cathode reaches an electron emitting temperaturewhich all toc frequently means the loss of the particular phenomenon thediagncstician desired to radiograph.

To avoid such time lapse, the present invention raises the temperatureoi the large focal spot cathode in the extremely short period of time ofone-tenth of a second or less. For this purpose an energy storagedevice, such as a condenser 46, is provided, which is arranged todischarge its energy through the cathode, in substantially the samemanner as shown and described in my application Serial No. 540,382,filed concurrently herewith, now Patent No. 2,420,844. As shown in thedrawing, the condenser 4l) is charged to a desired potential from anysuitable direct current source properly insulated from the high voltage,as indicated by the legend in the iigures. One such source may comprisea transformer and rectifying bridge arrangement, such as that shown forenergizing the X-ray tube, but natura-lly of a much lower voltage thanthat of the high voltage transformer 9.

The discharge circuit for thev condenser 40 includes, in addition to thelarge focal-spotcathode 8, a three electrode control tube 42 having itscathode-anode circuit included in series with the condenser 46 andcathode 8. This tube 42 normally prevents discharge of the condenser 45since its control electrode is supplied with a biasing potential from asource, such as a battery 43 and resistance 44, which is more negativethan that supplied to the cathode of the tube 42. For controllingdischarge oi condenser 4t by rendering the tube 42 conductive, itscathode and control electrode are connected to the secondary winding 45of an insulation transformer 4E through a resistance 41.

The primary winding 48 of the insulation transformer 46 is included inthe discharge circuit oi a further condenser 49, also charged from asuitable direct current source in the same manner as that for thecondenser 4U, as previously mentioned. Discharge of this lattercondenser 49 is also normally prevented by a three element control tube5U similar to the tube 42. The control tube 56 likewise has a biasingpotential applied to its control electrode from a suitable source, suchas a battery 52 through resistances 53 and Sii, which is more negativethan that applied to its cathode.

In order to render the tube 55 conductive, a further source such as abattery or the like 55 is provided which is connected to the cathode andcontrol electrode by closure of a contact 56 of relay 36. Upon closureof this contact 56, the potential supplied to the control electrode oftube 5U is then made more positive than that supplied to the cathode bythe battery 55, thus overcoming the bias supplied by the source, such asthe battery 52, and immediately rendering tube 5G conductive. Thiscauses condenser 49 to discharge through the primary Winding 48 ofinsulation transformer lit. The resulting energy impulse is induced inthe secondary winding 45, which in turn is impressed across thecathodecontrol electrode of the trigger tube 42, which thus overcomesthe negative bias impressed thereacross from the source 43 and makingthis tube conductive. This immediately causes the condenser 46 todischarge its stored energy through the large focal-spot cathode 8.

t is also to be noted that since the relay contact 56 closes itscontacts simultaneously with the short-circuiting of the adjustableresistance 29 by closure of relay contact 37, the discharge of condenser4B occurs simultaneously with the supply of increased energy from thesecondary winding l1. Discharge of the condenser 4i] occurs inapproximately 0.1 of a second (although this time can be shortenedbyincreasing the voltage or capacity of the condenser, as described in theabove noted copending application), which thusraises the lamentarycathode 8 to an electron emitting temperature in the same period of timewith the cathode then being maintained at such electron emittingtemperature by the energy supplied from the secondary winding I'I. Y

.'pon .the cathode 8` thus reaching Aan electron emitting temperature,X-rays are generated for the time period for which the high tensiontransformer 9 is energized under the control of the usual timer and thedesired exposure is made, The large focal-spot cathode 8 is accordinglyraised to an electron emitting temperature very rapidly, i. e. in about0.1,second or less, in lieu of the longer time of approximately onesecond as heretofore required. Since the time required for change-over fthe apparatus from fluoroscopic to radiographic purposes is s0 greatlyreduced, the phenomenon observed during a fluoroscopi'c examination canbe readily radiographed before a change or alteration of such phenomenonoccurs, as too frequently results in cases of human organs during theirnatural function, which cannot be accomplished with apparatus heretoforeknown t0 the art,

Having completed a radiographic exposure, the apparatus is again readilychanged over for ucroscopic purposes by momentarily opening the switch34, which, as above mentioned, may be operated by movement of thecassette out of the field of radiation from the X-ray tubeJ or by hand.Momentary opening of the switch 34 interrupts the self-holding circuitto the winding 35 of relay 36 causing its armature to gravitate and itsnormally open contacts 31 and 56 to again assume their open position andthe normally closed contact 2 to again close. The closure of contact 26accordingly completes the circuit to the primary winding I9, thus againenergizing the small focal-spot cathode l and at the same time openingof contact 3l interrupts the short-circuit for the adjustable resistance.29, causing the latter to again limit the energy supplied by secondarywinding Il to the large focal-spot cathode 8, whereby its temperature ismaintained below electronemission.

In Fig. 2 a slight modication of the present invention is shown whichdiiers from that previously described in the manner of control. Forexample, in Fig. 2 the points A--B and X-Y correspond to the same pointsin Fig. 1 so that it will be seen that one end of each of the lowvoltage primary windings i9 and 28 are connected directly to theconductor 2l and constituting one side of the supply source Ll.conductor 2li in this modification connects to a double-throw switch orthe like 6d, which in one position completes a circuit to primarywinding i9 of low tension transformer I5, thus causing the secondarywinding l5 to energize the small focal-spot cathode Similarly, movementci the switch 6i) (which again may be actuated by movement of thecassette as previously mentioned) into its other position completes acircuit to the primary winding 28 of low tension transformer I8 causingits secondary winding Il to energize the large focalspot cathode 8raising it to an electron emitting temperature. At the same time,however, energization of secondary winding il also causes discharge ofcondenser 4G through the cathode 8 to suddenly raise the temperature ofthe latter in'the manner previously described. In the modication of Fig.2 it will be noted, however, that the large focal-spot cathode 8 is notpreheated (although it may be if desired), and the energization of thetransformer i8 also controls the simultaneous discharge of condenser 4S.

The latter is accomplished in the following manner: The trigger tube 42is included in the discharge circuit of condenser 40 along with the The6. cathode 8, and the control electrode-cathode'is supplied with abiasing potential from the battery 43 through resistance 44, in theidentical manner as described relative to Fig. 1. However.,

instead of the control electrode-cathode of tube 42 being connected toan insulating transformer 46 and a control arrangement as in Fig. 1, thecontrol electrode-cathode in this latter modification is connectedthrough resistances 62 and 6'3 to the secondary winding Il'oftransformer I8. Consequently, upon closure of switch 60 to theradiographic position, with attendant energization of the largefocal-spot cathode 8, the Voltage of the secondary winding l1 is appliedthrough the resistances 62 and 63 across the control electrode andcathode of the trigger tube 42.

This immediately changes the biasing potential of the control electrodeas supplied by the battery 43 from more negative with respect to thecathode to a more positive biasing potential with respect to the cathodemaking the tube immediately conductive, thus causing the condenser 4l)to discharge through the large focal-spot cathode 8, as mentioned above.The modication of Fig. 2 thus dispenses not only with the necessity foran insulation transformer, such as 46, but also eliminates the remainderof-the control arrangement of Fig. 1, including the additional controltube 5S and condenser 49, together with the various sources of supply,as well as a multi-contact relay 36 as shown in Fig. 1.

lt thus becomes obvious to those skilled in the art that an X-rayapparatus is herein provided for double-focus X-ray tubes wherein theapparatus is rapidly converted from its setting for fiuoroscopicpurposes to a radiographic setting. Moreover, the change-over from thesmall focalspot cathode to the large focal-spot cathode is accompaniedby substantially no time lag in the large focal-spot cathode reaching anelectron emitting temperature. This is effected by discharging an energystorage means such as a condenser through the filamentary cathode whichraises the latter to an electron emitting temperature in 0.1 of a secondor less depending upon the voltage across the condenser.

Although two embodiments of the present invention have been shown anddescribed, it isfto be understood that still further modications thereofmay be made without departing from the spirit and scope of the appendedclaims.

I claim:

1. An X-ray apparatus for the making of fluoroscopic and radiographicexaminations comprising an Y-ray tube provided with a small focal-spotproducing cathode and a large focalspot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means'for heating saidsmall focal-spot producing `cathode to an electron emitting temperaturefor uoroscopic purposes, means operable to cause substantiallyinstantaneous heating of said large focal-spot producing cathode to anelectronemitting temperature for radiographic purposes, and meansoperable to interrupt the heating of said small focal-spot producingcathode and to cause the immediate operation of said last vmentionedmeans with attendant instantaneous heating of said large focal-spotproducing cathodefrom' a source of supply independent of the means forheating the small focal-spot producing cathode.

2. An X-ray apparatus for the making of fluoroscopic and radiographicexaminations coinprising an X-ray tube providedwith a smallifo- 7cal-spot producing cathode and a large focalspot producing cathode, asource of electrical energy for energizing said X-ray tube, means forheating said small focal-spot producing cathode to an electron emittingtemperature for fluoroscopic purposes, means operable to cause theraising of said large focal-spot producing cathode to an electronemitting temperature in 0.1 of a second or less for radiographicpurposes, and means operable' to interrupt the heating of said smallfocal-spot producing cathode and to cause the immediate operation ofsaid last mentioned means with attendant instantaneous heating of saidlarge focal-spot producing cathode from a source of supply independentof the means for heating the small focal-spot producing cathode.

3. An X-ray apparatus for the making of fluoroscopic and radiographicexaminations comprising an X-ray tube provided with a small focal-spotproducing cathode and a large focal-spot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means for heating saidsmall focal-spot producing cathode to an electron emitting temperaturefor iluoroscopic purposes, means operable to cause the momentaryapplication of a source of energy to said large focal-spot producingcathode having a magnitude in excess of that required to maintain thelatter at an electron emitting temperature to suddenly raise the largefocal-spot producing cathode to an electron emitting temperature withoutan appreciable time lapse for purposes of radiography, and meansoperable to interrupt the heating of said small focal-spot producingcathode and to cause the immediate operation of said last mentionedmeans with attendant sudden heating of said large focal-spot producingcathode from a source of supply independent of the means for heating thesmall focal-spot producing cathode.

4. An X-ray apparatus for the making of fluoroscopic and radiographicexaminations comprising an X-ray tube provided with a small focal-spotproducing cathode and a large focalspot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means for heating saidsmall focal-spot producing cathode to an electron emitting temperaturefor fluoroscopic purposes, energy storage means having a magnitude ofelectrical energy in excess of that required to maintain said largefocal-spot producing cathode at an electron emitting temperature, andmeans operable to interrupt the heating of said small focal-spotproducing cathode and to simultaneously cause the momentary discharge ofsaid energy storage means directly through said large focal-spotproducing cathode to suddenly raise the latter to an electron emittingtemperature for purpose of radiography.

5. An X-ray apparatus for the making f iluoroscopic and radiographicexaminations comprising an X-ray tube provided With a small focal-spotproducing cathode and a large focalspot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means for heating saidsmall focal-spot producing cathode to an electron emitting temperaturefor fluoroscopic purposes, means for heating said large focal-spotproducing cathode to a temperature where no appreciable electronemission occurs, means operable to apply an energy impulse directly tosaid large focal-spot producing cathode of a magnitude in excess of thatavailable from said last mentioned means to suddenly raise the largefocal-spot producing cathode to an electron emitting temperature Withoutan appreciable time lapse for purposes of radiography, and meansoperable to interupt heating of said small focal-spot producing cathodeand to cause the simultaneous operation of said last mentioned meanswith attendant application of an energy impulse to said large focal-spotproducing cathode from a source of supply independent of the means forheating the small focal-spot producing cathode.

6. An X-ray apparatus for the making of fluoroscopic and radiographicexaminations comprising an X-ray tube provided with a small focal-spotproducing cathode and a large focalspot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means for heating saidsmall focal-spot producing cathode to an electron emitting temperaturefor fluoroscopic purposes, means independent of said means for heatingsaid small focal-spot producing cathode for normally heating said largefocal-spot producing cathode to a temperature Where no appreciableelectron emission occurs but adapted to raise and maintain the same atan electron emitting temperature, energy storage means of a magnitudegreater than said last mentioned means and adapted to directly dischargeits accumulated energy through said large focalspot producing cathode,and means operable to interrupt the heating of said small focal-spotproducing cathode and to simultaneously cause said last mentioned meansto heat said large focal-spot producing cathode to an electron emittingtemperature together with momentary disl charge of said energy storagemeans through the latter to suddenly raise the large focal-spotproducing cathode to an electron emitting temperature without anappreciable time lapse for purposes of radiography.

7. An X-ray apparatus for the making of iiuoroscopic and radiographicexaminations comprising an X-ray tube provided with a small focal-spotproducing cathode and a large focalspot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means for heating saidsmall focal-spot producing cathode to an electron emitting temperaturefor fluoroscopic purposes, a low potential transformer independent ofsaid means for heating said small focal-spot producing cathode forheating said large focal-spot producing cathode, an impedance device fornormally limiting the energy supplied by said transformer to said largefocal-spot producing cathode to maintain the latter at a temperaturewhere no appreciable electron emission occurs, energy storage meanshaving a magnitude of energy greater than that of said transformer andadapted to momentarily discharge its accumulated energy directly throughsaid large focal-spot producing cathode, and means operable to interruptthe heating of said small focal-spot producing cathode and tosimultaneously cause the short-circuiting of said variable impedance anddischarge of said energy storage means to suddenly raise the largefocal-spot producing cathode to an electron emitting temperature Withoutan appreciable time lapse for purposes of radiography.

8. An X-ray apparatus for the making of uoroscopic and radiographicexaminations comprising an X-ray tube provided with a small Iocal-spotproducing cathode and a large focalspot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means for heating saidsmall focal-spot producing cathode to an electron emitting temperaturefor fluoroscopic purposes, energy storage means having .a magnitude ofelectrical energy in excess of that required to maintain said largefocal-spot producing cathode at an electron emitting temperature, and aswitch operable to cause interruption of the heating of said smallfocal-spot producing cathode and to cause the momentary discharge ofsaid energy storage means directly through said large focal-spotproducing cathode to. suddenly raise the latter to an electron emittingtemperature for purposes of radiography.

9. An X-ray apparatus for the making of fluoroscopic and radiographicexaminations comprising an X-ray tube provided with a small focal-spotproducing cathode and a large focalspot producing cathode, a source ofelectrical energy for energizing said X-ray tube, means for heating saidsmall focal-spot producing cathode to an electron emitting temperature:for` luoroscopic purposes, a low potential transformer independent ofsaid means for heating said small focal-spot producing cathode forheating said large focal-spot producing cathode, an impedance device fornormally limiting the energy supplied by said transformer to said largefocal-spot producing cathode to maintain the latter at a temperaturewhere no appreciable electron emission occurs, energy storage meanshaving a magnitude of energy greater than that of said transformer, acontrol tube normally operable to prevent discharge of said energystorage means, and a switch operable to cause interruption of theheating of said small focal-spot producing cathode and short-circuitingof said impedance and to cause said control tube to become conductivewith attendant momentary discharge of said energy storage means directlythrough said large focalspot producing cathode to suddenly raise thelatter to an electron emitting temperature for purposes of radiography.

CHARLES M. SLACK.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Eaton Apr. 29, 1941

